1. Field of the Invention
The invention relates to the spectral analysis of wood, and in particular to a method of predicting mechanical properties of decayed wood that has been exposed to microorganisms by using light in a selected range of a visible and near infrared (VIS-NIR) spectrum.
2. Description of the Prior Art
A method for the nondestructive analysis of the quality of a tree, unlike conventional methods, which measure the volume and form of a tree, would provide important information to assist woodland owners in making their thinning decisions, and in the valuation of a stand of timber. The method would also be useful in the analysis of trees or sawn logs, in the woods, for the field sorting of logs to be used as poles, feedstocks in the manufacture of veneers, lumber or chips, or for measuring the strength of pole or wood used in utilities or structures.
Near infrared (NIR) spectroscopy, in combination with multivariate analysis (MVA) tools, is currently in use for the characterization of complex systems. These several statistical methods are also termed chemometric methods, forming the discipline of chemometrics, when applied generally to the field of chemistry, and in particular to the field of analytical chemistry. The technique of chemometrics is more fully explained in Brown, S. D., xe2x80x9cChemometricsxe2x80x9d, Anal. Chem. 62, 84R-101R (1990).
Also, near-infrared spectroscopy and chemometrics have been described for use in the non-destructive analysis of the chemical and physical properties of paper.
For example, U.S. Pat. No. 5,638,284 describes a method for the measurement of the wet strength of paper by analyzing the visible, near-infrared and/or infrared spectrum of the paper/pulp in the process line using a wavelength range within 400 nm to 4,000 nm, and applying a chemometric evaluation of the spectrum, to calculate the wet strength of the paper. Other examples include U.S. Pat. No. 5,680,321 (determining physical properties selected from dry tensile strength, hydrophobicity, debonding energy, bursting strength, wettability and printability in paper), and U.S. Pat. No. 5,680,320 (quantifying the amounts of reacted and/or retained chemical additives in paper by analysis of the visible, near-infrared and/or infrared spectrum of the paper/pulp in a process line).
While the foregoing art discloses the use of chemometric evaluation in the analysis of paper products, the entire NIR spectral range between 400 nm and 4,000 nm is used for the evaluation. Also, the mechanical properties of wet-solid-wood samples or wet or dry decayed wood are much more complex than those of paper due, in part, due to the presence of high concentrations of hemicellulose and lignin in wood relative to these components in paper. The structure and macromolecular morphology of the sample, such as roughness, color, and grain orientation also affect the spectral properties of solid wood. For a wet wood sample, the analysis of these properties is problematic because moisture in the samples, along with the high concentrations of lignin and hemicellulose tends to block or conceal the spectrometric derived information. Furthermore, many of these paper properties are a direct result of the presence of a small amount of an additive, or size or wet-strength resin, rather than a function of the inherent properties of paper fibers.
One example of the characterization of the NIR wood is described in U.S. Pat. No. 5,965,888, in which, NIR spectrometric data are obtained from dried wood chips. The method for the determination of parameters of wood panels comprises analyzing the raw wood chips/panels at a moisture content  less than 10% by a spectrometric method to provide spectral data, and comparing the spectral data with reference spectral data from a reference chip/panel calibrated to known parameters of panels produced from the reference material, or of the reference panel by multivariate analysis. Again this method relies on the entire spectral range. This method is useful in predicting the quality of a dry wood panel based on an analysis of dried wood chips which are used as a feedstock in the manufacturing process.
NIR has also been used for determination of surface roughness and fiber angle of dry wood relative to the duration of the incident light, and for the evaluation of density and the strength of wood from a dry sample. See, e.g., Hoffmeyer, P., et al., Holz als Roh-und Werkstoff 53 (1995) 165-170.
In both U.S. Pat. No. 5,965,888 and Hoffmeyer, P., et al., Holz als Roh-und Werkstoff 53 (1995) 165-170, reference is explicitly made to the problems associated with measuring the NIR properties of wet wood, and seek to overcome them with use of a dry sample for analysis. All of these references use the full NIR spectral range, generally considered to be between 400 and 2,500 nm. Thus, they are using information from more than 2,000 individual wavelengths.
U.S. Pat. No. 5,945,676 disclose a method and apparatus for multi-spectral analysis in non-invasive NIR spectroscopy in which incident radiation containing a plurality of distinct, nonoverlapping spectral regions of wavelengths is used to irradiate the sample. Diffusively reflected radiation emerging from the sample is detected, and a value indicative of the concentration of the analyte is obtained, preferably using an application of chemometrics techniques.
A hand-held device for infrared reflectance measurements of samples to identify the sample material and comprising a self-contained portable unit built into a hand held housing is disclosed in U.S. Pat. No. 6,031,233. The housing includes a window and optics on a bench adjacent to the window, so that the optics are aligned with the sample when the device is placed directly against the sample. The optics include a broad-band IR light source shining onto an acousto-optic tunable filter (AOTF), which passes narrow-band IR light with a swept frequency; a lens focussing the radiation IR through the window onto the sample; and a reflectance detector aligned with the window of the housing to pick up reflected light. A computer, which may be mounted in the housing, compares the detected reflectance spectrum with stored sample data spectra, and identifies the material or the components of the material and their proportions.
However, none of the foregoing references are directed to measuring the mechanical properties of decayed wood that has been exposed to wood decay organisms, rather than changes in the chemical composition which are known to change as wood is decayed by microorganisms. And in many cases this decayed wood is also wet which further complicates the analysis.
A need therefore exists to measure the mechanical properties of decayed wood that has been exposed to microorganisms for predicting the serviceability and reliability of wood structures.
One object of the present invention is to provide a method for measuring the mechanical properties of decayed wood that has been exposed to microorganisms to enable predicting the serviceability and reliability of wood structures.
Another object of the present invention is to provide a method for measuring the mechanical properties of wood frames in houses and buildings, and wood poles used to support telephone, power lines, and marine structures that have been exposed to microorganisms that cause wood decay to enable predicting the serviceability and reliability of these wood frames and poles.
A further object of the present invention is to provide a practical device that can be used to collect and process VIS-NIR spectral data in a rapid and low cost method for measuring mechanical properties of decayed wood that has been exposed to microorganisms to enable predicting the serviceability and reliability of wood structures.
A still further object of present invention is to provide a process of utilizing VIS-NIR spectrum from about 400 to about 1,150 nm for measuring the strength of decayed wood that has been exposed to microorganisms that cause wood decay.
In general, the invention process is accomplished by gathering VIS-NIR spectra of wood that has been exposed to decayed organisms, and whose mechanical strength has been measured by some common analytical technique; using a first step where VIS-NIR spectra and mechanical strength values are used to construct a calibration model using multivariate statistical techniques; and using a second set of VIS-NIR spectra gathered from wood that has been exposed to decayed organisms, but whose strength is not known, and combining these spectra with the calibration model to predict the strength of the samples in the second set.